Method and apparatus for recovery of metals with hydrocarbon-utilizing bacteria

ABSTRACT

Methods and apparatus are disclosed for recovering metals from metal-containing support materials such as mineral ores. In one embodiment, the metal may be separated from crushed support material or ore in a bioleaching lagoon by the action of hydrocarbon-utilizing bacteria under anaerobic conditions. The bioleached material is then pumped into a precipitation lagoon where hydrocarbon-utilizing bacteria oxidize the metals under aerobic conditions. In another embodiment, metals may be directly biooxidized from a heap of the metal-containing support material having a hydrocarbon/oxygen injection system embedded therein. A water sprinkler system may be used to wet the heap while the hydrocarbon/oxygen injection system stimulates the growth of hydrocarbon-utilizing bacteria. The resulting effluent solution may be pumped or gravity fed to an aerobic precipitation lagoon where aerobic hydrocarbon-utilizing bacteria are used to precipitate or otherwise deposit the metals onto a deposition material.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication Serial No. 60/308,211, filed Jul. 27, 2001, which isincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to the recovery of metals frommetal-containing support materials, and more particularly relates to amethod and apparatus for recovering metals from support materials withhydrocarbon-utilizing bacteria.

BACKGROUND INFORMATION

[0003] Precious metal ores such as gold ores can be categorized aseither free milling or refractory. Free milling ores are those that canbe processed by simple gravity techniques or direct cyanidation.Refractory ores, on the other hand, are not amenable to conventionalcyanidation treatment. Such ores are often refractory because of theirexcessive content of metallic sulfides such as pyrite or organiccarbonaceous matter. A large number of refractory ores consist of oreswith a precious metal such as gold occluded in iron sulfide particles.The iron sulfide particles consist principally of pyrite andarsenopyrite. If gold or other precious metals remain occluded withinthe sulfide host, even after grinding, then the sulfides must beoxidized to liberate the encapsulated precious metal values and makethem amenable to a leaching agent.

[0004] Conventional biological methods have focused on the recovery ofprecious metals using sulfur-oxidizing bacteria. A conventional processincludes the steps of distributing a concentrate of refractory sulfideminerals on top of a heap of material, biooxidizing the concentrate ofrefractory sulfide minerals, leaching precious metal values from thebiooxidized refractory sulfide minerals with a lixiviant, and recoveringprecious metal values from the lixiviant.

[0005] Problems exist using sulfur-oxidizing organisms in bioleachingprocesses. These problems include nutrient access, air access, carbondioxide access, the generation of sulfuric acid from reactions of thesulfur-oxidizing bacteria, and the generation of heat during theexothermic biooxidation reactions which can kill growing bacteria. Oresthat are low in sulfide or pyrite, or ores that are high in acidconsuming materials such as calcium carbonate or other carbonates, mayalso be problematic during heap biooxidation processes. The acidgenerated by these low pyrite ores is insufficient to maintain the lowpH and high iron concentration needed for bacteria growth.

[0006] The bioremediation of various pollutants using butane-utilizingbacteria is disclosed in U.S. Pat. Nos. 5,888,396, 6,051,130, 6,110,372,6,156,203, 6,210,579, 6,244,346 and 6,245,235, which are hereinincorporated by reference.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention, metals such as preciousmetals are recovered from metal-containing support materials such asmineral ores. The support material is contacted with a solutioncontaining a hydrocarbon which stimulates the growth ofhydrocarbon-utilizing bacteria. The hydrocarbon may comprise one or morealkanes, such as butane, methane, ethane and/or propane, or other typesof hydrocarbons.

[0008] Gold, silver, platinum, copper, zinc, nickel, uranium, palladiumand the like may be recovered using the present invention. Oneembodiment of the present invention provides for the treatment ofmetal-containing support materials in the form of slurries contained inlagoons, tanks or other vessels. Another embodiment of the presentinvention provides a bioleaching technique, which initially useshydrocarbon-utilizing bacteria under anaerobic conditions to pretreatore-containing materials for subsequent biooxidation usinghydrocarbon-utilizing bacteria under aerobic conditions. The process canbe used to biooxidize metal-containing support materials such asprecious metal-bearing refractory sulfide ores. A further embodiment ofthe present invention provides a heap bioleaching process. In oneembodiment of this process, ores that are low in sulfide minerals, orores that are high in acid consuming materials such as calciumcarbonate, may be treated.

[0009] In addition to precious metal-bearing sulfide minerals, there aremany other sulfide ores that can be treated using the present process,such as copper ores, zinc ores, nickel ores and uranium ores.Biooxidation with hydrocarbon-utilizing bacteria can be used to causethe dissolution of metal values such as copper, zinc, nickel and uraniumfrom concentrates of these ores.

[0010] An aspect of the present invention is to provide a method ofrecovering a metal from a metal-containing support material. The methodincludes contacting the support material with a hydrocarbon to stimulatethe growth of hydrocarbon-utilizing bacteria, and recovering the metalfrom the support material.

[0011] Another aspect of the present invention is to provide a systemfor recovering metal from a metal-containing support material. Thesystem includes means for contacting the support material with ahydrocarbon to stimulate the growth of hydrocarbon-utilizing bacteria,and means for recovering the metal from the support material.

[0012] A further aspect of the present invention is to provide a systemfor metal recovery from a support material, wherein the system includesa source of hydrocarbon, a hydrocarbon injection system in communicationwith the hydrocarbon source and the support material, and a depositionmaterial upon which the metal is deposited.

[0013] These and other aspects of the present invention will be moreapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic diagram illustrating the use of anaerobicand aerobic hydrocarbon-utilizing bacteria to bioleach and precipitate(biooxidize) metals from a metal-containing support material.

[0015]FIG. 2 is a schematic diagram illustrating the use of aerobichydrocarbon-utilizing bacteria in a heap to biooxidize and precipitatemetals from a metal-containing support material.

DETAILED DESCRIPTION

[0016] In accordance with the present invention, hydrocarbon-utilizingbacteria are used to liberate metals from metal-containing supportmaterials such as mineral ores. The process may be used to biooxidizemetals from ore-containing material using hydrocarbons under aerobicconditions only. Alternatively, the process may use anaerobic andaerobic processes to pretreat and biooxidize metals from ore-containingmaterials. The ore type and metal composition may determine whichprocess would yield the most favorable metal recover. Under anaerobicconditions, the hydrocarbon may serve as an electron donor and carbonsource while sulfate originating from the ore may serve as a finalelectron acceptor. Other electron acceptors may be used, such asnitrate, iron or carbon dioxide. Subsequently, aerobichydrocarbon-utilizing organisms and their operative enzymes may be usedto precipitate metals from solution, which may then be recovered.

[0017] In accordance with an embodiment of the present invention, ahydrocarbon such as butane may be utilized to drive a treatment processanaerobic, thereby encouraging the growth of anaerobic microorganismscapable of reducing sulfur-containing compounds. Under anaerobicconditions, sulfate and elemental sulfur may serve as electron acceptorswhile the hydrocarbon substrate is oxidized. The anaerobic processes mayinclude, for example, desulfurization, sulfur respiration anddissimilatory sulfate reduction. A hydrocarbon such as butane may beused to enhance anaerobic microbiological processes thereby liberatingprecious metals from recalcitrant sulfide ore bodies. Subsequently,aerobic hydrocarbon-utilizing bacteria may be used to precipitate(biooxidize) metals from solution, which may then be recovered.

[0018] The metal-containing support material may includesulfide-containing mineral ores, such as precious metal-containing ores,copper ores, zinc ores, nickel ores and uranium ores. Thesulfide-containing minerals and ore material may be, for example,coarsely or finely ground ore. The support material may also includelava rock, gravel, sand deposits or any other geologic materials. Therecovered metals may include gold, silver, platinum, palladium, copper,zinc, nickel and uranium or any other metal or precious metal.

[0019] The hydrocarbon may comprise one or more alkanes, alkenes,alkynes, poly(alkene)s, poly(alkyne)s, aromatic hydrocarbons, aromatichydrocarbon polymers or aliphatic hydrocarbons. The hydrocarbonspreferably comprise at least one alkane such as butane, methane, ethaneor propane. In a preferred embodiment, the hydrocarbon comprises butanewhich may serve as an electron donor under aerobic or anaerobicconditions. The high solubility of butane facilitates dispersion of thehydrocarbon food source throughout the metal-containing supportmaterial. Furthermore, the high solubility of butane may accelerate thetransformation of aerobic conditions to anaerobic by initiallystimulating the growth of aerobic butane-utilizing microorganisms in thepresence of oxygen to produce carbon dioxide. As the oxygen is depletedand anaerobic conditions prevail, butane or another hydrocarbon mayserve as an electron donor to enhance anaerobic microbiologicalprocesses that will aid in the leaching of metals from themetal-containing support material.

[0020] In accordance with a preferred embodiment, butane is the mostprevalent compound of the hydrocarbon substrate on a weight percentbasis, and typically comprises at least about 10 weight percent of thehydrocarbon substrate. The other constituents of the hydrocarbonsubstrate may include other alkanes or other hydrocarbons, as well asinert gases such as nitrogen, helium or argon. The hydrocarbon substratepreferably comprises at least about 50 weight percent butane. Morepreferably, the hydrocarbon substrate comprises at least about 90 weightpercent butane. In a particular embodiment, the hydrocarbon substratecomprises at least about 99 weight percent n-butane. The butane maycontain straight (n-butane) and/or branched chained compounds such asiso-butane.

[0021] Suitable hydrocarbon-utilizing bacteria may include the followingGroups (in addition to fungi, algae, protozoa, rotifers and otheraerobic and anaerobic microbial populations found in decayingmaterials):

[0022] Group 1: The Spirochetes

[0023] Group 2: Aerobic/Microaerophilic, motile, helical/vibroid,gram-negative bacteria

[0024] Group 3: Nonmotile (or rarely motile), gram-negative bacteria

[0025] Group 4: Gram-negative aerobic/microaerophilic rods and cocci

[0026] Group 5: Facultatively anaerobic gram-negative rods

[0027] Group 6: Gram-negative, anaerobic, straight, curved, and helicalbacteria

[0028] Group 7: Dissimilatory sulfate- or sulfur-reducing bacteria

[0029] Group 8: Anaerobic gram-negative cocci

[0030] Group 10: Anoxygenic phototrophic bacteria

[0031] Group 11: Oxygenic phototrophic bacteria

[0032] Group 12: Aerobic chemolithotrophic bacteria and associatedorganisms

[0033] Group 13: Budding and/or appendaged bacteria

[0034] Group 14: Sheathed bacteria

[0035] Group 15: Nonphotosynthetic, nonfruiting gliding bacteria

[0036] Group 16: The fruiting, gliding bacteria and the Myxobacteria

[0037] Group 17: Gram-positive cocci

[0038] Group 18: Endospore-forming gram-positive rods and cocci

[0039] Group 19: Regular, nonsporing, gram-positive rods

[0040] Group 20: Irregular, nonsporing, gram-positive rods

[0041] Group 21: The mycobacteria

[0042] Groups 22-29: The actinomycetes

[0043] Group 22: Nocardioform actinomycetes

[0044] Group 23: Genera with multiocular sporangia

[0045] Group 24: Actinoplanetes

[0046] Group 25: Streptomycetes and related genera

[0047] Group 26: Maduromycetes

[0048] Group 27: Thermomonospora and related genera

[0049] Group 28: Thermoactinomycetes

[0050] Group 29: Genus Glycomyces, Genus Kitasatospira and GenusSaccharothrix

[0051] Group 30: The Mycoplasmas—cell wall-less bacteria

[0052] Group 31: The Methanogens

[0053] Group 32: Archaeal sulfate reducers

[0054] Group 33: Extremely halophilic, archaeobacteria (halobacteria)

[0055] Group 34: Cell wall-less archaeobacteria

[0056] Group 35: Extremely thermophilic and hyperthermophilicS⁰-metabolizers.

[0057] In addition, suitable bacteria may include facultative anaerobesand microaerophilic anaerobes, which are capable of surviving at lowlevels of oxygen. These bacteria do not require strict anaerobicconditions such as the obligate anaerobes. Acidophilic, alkaliphilic,anaerobe, anoxygenic, autotrophic, chemolithotrophic, chemoorganotroph,chemotroph, halophilic, methanogenic, neutrophilic, phototroph,saprophytic, thermoacidophilic, and thermophilic bacteria may be used.Hydrocarbon and oxygen injection may encourage the growth of othermicroorganisms such as fungi, protozoa and algae that may be beneficialto the metal recovery process. The injected oxygen may be in the form ofair (e.g., dry air comprising 20.9 percent oxygen), a gas stream withvarying concentrations of oxygen, substantially pure oxygen, or thelike.

[0058] Recovery of the metal involves the removal of at least a portionof the metal contained in or on the metal-containing support material.For example, from about one percent to substantially all of the metalcontained in the support material may be recovered. Recovery may beachieved using various techniques such as heaps, slurries, precipitationlagoons and bioreactors. During the treatment process, metals may bedeposited on a metal deposition material comprising, for example, apolymer, felt, rubber, metallic or natural fiber material that is porousor non-porous. The deposition material may be provided in sheet form orin other forms that provide increased surface area such as spheres andother geometric shapes.

[0059]FIG. 1 schematically illustrates an anaerobic and aerobic metalrecovery system 10 in accordance with an embodiment of the presentinvention. A metal-containing support material such as low grade ore 12is fed to a rock crusher 14. Crushed ore 16 from the rock crusher 14 isfed to a bioleaching lagoon 18 lined with a membrane 19 and equippedwith mixers 20 and 21. A source of hydrocarbon 22 such as butane isconnected to hydrocarbon injectors 24 in the bioleaching lagoon 18.

[0060] After treatment in the bioleaching lagoon, the material is pumped26 to a precipitation lagoon 28 equipped with mixers 30 and 31. Ahydrocarbon/oxygen source 32 is connected to injectors 34 in theprecipitation lagoon 28. A membrane 36 lines the precipitation lagoon28. After treatment in the lagoon 28, liquid 38 comprising water and thesupport material is removed from the precipitation lagoon 28. Metaldeposited on the membrane liner 36 may be recovered from theprecipitation lagoon 28 at suitable intervals.

[0061] In the embodiment shown in FIG. 1, the first phase of the metalrecovery process occurs in the bioleaching lagoon 18 under anaerobicconditions. Within the lagoon 18, the metal-containing support materialis contacted with the hydrocarbon to accelerate the transformation ofaerobic conditions to anaerobic conditions. This is accomplished byinitially accelerating the activity of aerobic hydrocarbon-utilizingbacteria in the presence of oxygen present in the lagoon 18 in order toproduce carbon dioxide. Under the resultant anaerobic conditions, thehydrocarbon will serve as an electron donor, thereby acceleratinganaerobic microbiological treatment processes. In the bioleachinglagoon, the crushed ore 16 is pretreated for subsequent recovery in theprecipitation lagoon. The second phase of the metal recovery processoccurs in the precipitation lagoon 28, where the aerobic cycle with airinjection may be used to accelerate metal precipitation.

[0062]FIG. 2 schematically illustrates an aerobic metal recovery system40 in accordance with another embodiment of the present invention. Aheap 42 comprising the metal-containing support material is subjected towater spray by a sprinkler system 44. A hydrocarbon/oxygen supply 46 isconnected to injectors 48 in the heap 42. An effluent trench 50 underthe heap 42 carries effluent to a precipitation lagoon 52 equipped withmixers 54 and 55. Alternatively, the effluent could be pumped to thelagoon 52. Another hydrocarbon/oxygen supply 56 is connected toinjectors 58 in the lagoon 52. A membrane liner 60 lines the lagoon 52.After treatment in the lagoon 52, liquid 62 comprising water and thesupport material is removed from the lagoon 52. Metal deposited on themembrane liner 60 may be recovered from the lagoon 52 at suitableintervals.

[0063] In the embodiment shown in FIG. 2, the heap 42 may comprise oredeposits. The piping 48 through which the hydrocarbon/oxygen mixture orhydrocarbon alone is delivered may be operated under steady orintermittent pulses. The sprinkler system 44 flushes the oxidized metalvalues from the heap 42 and creates an effluent solution, which flows tothe precipitation lagoon 52. In the precipitation lagoon 52, thehydrocarbon-utilizing bacteria and injected oxygen deposit the metalvalues onto the membrane deposition material 60 for recovery.

[0064] Based on the molecular weight of specific metals, the differentmetal precipitate out of solution at differing time intervals, therebyproviding the opportunity to replace the membrane liners duringsuccessive depositional events. Alternatively, electrolysis methods maybe employed to further separate the precipitating metals. The metals maythen be easily assayed and further refined using conventionaltechniques.

[0065] Whereas particular embodiments of this invention have beendescribed above for purposes of illustration, it will be evident tothose skilled in the art that numerous variations of the details of thepresent invention may be made without departing from the invention.

What is claimed is:
 1. A method of recovering a metal from ametal-containing support material, the method comprising: contacting thesupport material with a hydrocarbon to stimulate growth ofhydrocarbon-utilizing bacteria; and recovering the metal from thesupport material.
 2. The method of claim 1, wherein the hydrocarboncomprises alkanes, alkenes, alkynes, poly(alkene)s, poly(alkyne)s,aromatic hydrocarbons, aromatic hydrocarbon polymers and/or aliphatichydrocarbons.
 3. The method of claim 1, wherein the hydrocarboncomprises at least one alkane.
 4. The method of claim 3, wherein the atleast one alkane comprises butane, methane, ethane and/or propane. 5.The method of claim 3, wherein the at least one alkane comprises butane.6. The method of claim 5, wherein the butane is provided as a butanesubstrate comprising butane as the most prevalent compound of thesubstrate on a weight percentage basis.
 7. The method of claim 5,wherein the butane is provided as a butane substrate comprising at leastabout 10 weight percent butane.
 8. The method of claim 5, wherein thebutane is provided as a butane substrate comprising at least about 50weight percent butane.
 9. The method of claim 5, wherein the butane isprovided as a butane substrate comprising at least about 90 weightpercent butane.
 10. The method of claim 5, wherein the butane isprovided as a butane substrate comprising at least about 99 weightpercent n-butane.
 11. The method of claim 3, wherein the at least onealkane comprises methane.
 12. The method of claim 3, wherein the atleast one alkane comprises ethane.
 13. The method of claim 3, whereinthe at least one alkane comprises propane.
 14. The method of claim 1,wherein the hydrocarbon and the support material are provided in asolution.
 15. The method of claim 14, wherein the solution compriseswater.
 16. The method of claim 1, wherein the hydrocarbon is introducedto the hydrocarbon-utilizing bacteria intermittently.
 17. The method ofclaim 1, wherein the hydrocarbon is introduced to thehydrocarbon-utilizing bacteria continuously.
 18. The method of claim 1,wherein the hydrocarbon-utilizing bacteria comprises aerobic bacteria,anaerobic bacteria, facultative anaerobes and/or microaerophilicanaerobes.
 19. The method of claim 1, wherein the hydrocarbon-utilizingbacteria comprise aerobic bacteria.
 20. The method of claim 1, whereinthe hydrocarbon-utilizing bacteria comprise anaerobic bacteria.
 21. Themethod of claim 1, wherein the hydrocarbon-utilizing bacteria compriseat least one bacterium selected from the group consisting ofPseudomonas, Variovorax, Nocardia, Chryseobacterium, Comamonas,Acidovorax, Rhodococcus, Aureobacterium, Micrococcus, Aeromonas,Stenotrophomonas, Sphingobacterium, Shewanella, Phyllobacterium,Clavibacter, Alcaligenes, Gordona, Corynebacterium and Cytophaga. 22.The method of claim 1, wherein the hydrocarbon-utilizing bacteriacomprise at least one bacterium selected from the group consisting ofputida, rubrisubalbicans, aeruginosa, paradoxus, asteroides,brasiliensis, restricta, globerula, indologenes, meningosepticum,acidovorans, delafieldii, rhodochrous, erythropolis, fascians, barkeri,esteroaromaticum, saperdae, varians, kristinae, caviae, maltophilia,thalpophilum, spiritivorum, putrefaciens B, myrsinacearum, michiganense,xylosoxydans, terrae, aquaticum B and johnsonae.
 23. The method of claim1, wherein the support material comprises a mineral ore.
 24. The methodof claim 1, wherein the support material comprises a refractory ore. 25.The method of claim 1, wherein the support material comprises a sulfidemineral ore.
 26. The method of claim 1, wherein the metal comprisesgold, silver, platinum, palladium, copper, zinc, nickel and/or uranium.27. The method of claim 1, further comprising introducing oxygen to thehydrocarbon-utilizing bacteria.
 28. The method of claim 27, wherein theoxygen is provided in the form of air or substantially pure oxygen. 29.The method of claim 27, wherein the oxygen is provided to thehydrocarbon-utilizing bacteria continuously.
 30. The method of claim 27,wherein the oxygen is provided to the hydrocarbon-utilizing bacteriaintermittently.
 31. The method of claim 1, wherein the metal isrecovered from the support material by precipitating the metal out of asolution comprising the support material.
 32. The method of claim 1,wherein the metal is recovered from the support material by depositingthe metal on a deposition material.
 33. The method of claim 1, whereinthe support material is provided in a heap.
 34. The method of claim 33,further comprising adding water to the heap.
 35. The method of claim 34,further comprising adding oxygen to the heap.
 36. A system forrecovering a metal from a metal-containing support material, the systemcomprising: means for contacting the support material with a hydrocarbonto stimulate growth of hydrocarbon-utilizing bacteria; and means forrecovering the metal from the support material.
 37. The system of claim36, wherein the hydrocarbon comprises alkanes, alkenes, alkynes,poly(alkene)s, poly(alkyne)s, aromatic hydrocarbons, aromatichydrocarbon polymers and/or aliphatic hydrocarbons.
 38. The system ofclaim 36, wherein the hydrocarbon comprises at least one alkane.
 39. Thesystem of claim 38, wherein the at least one alkane comprises butane,methane, ethane and/or propane.
 40. The system of claim 38, wherein theat least one alkane comprises butane.
 41. The system of claim 40,wherein the butane is provided as a butane substrate comprising butaneas the most prevalent compound of the substrate.
 42. The system of claim40, wherein the butane is provided as a butane substrate comprising atleast about 10 weight percent butane.
 43. The system of claim 40,wherein the butane is provided as a butane substrate comprising at leastabout 50 weight percent butane.
 44. The system of claim 40, wherein thebutane is provided as a butane substrate comprising at least about 90weight percent butane.
 45. The system of claim 38, wherein the at leastone alkane comprises methane.
 46. The system of claim 38, wherein the atleast one alkane comprises ethane.
 47. The system of claim 38, whereinthe at least one alkane comprises propane.
 48. The system of claim 36,wherein the hydrocarbon is introduced to the hydrocarbon-utilizingbacteria intermittently.
 49. The system of claim 36, wherein the metalis selected from the group comprising gold, silver, platinum, palladium,copper, zinc, nickel and/or uranium.
 50. A system for recovering a metalfrom a metal-containing support material, the system comprising: asource of hydrocarbon; a hydrocarbon injection system in communicationwith the hydrocarbon source and the support material; and a depositionmaterial upon which the metal is deposited.
 51. The system of claim 50,wherein the hydrocarbon comprises alkanes, alkenes, alkynes,poly(alkene)s, poly(alkyne)s, aromatic hydrocarbons, aromatichydrocarbon polymers and/or aliphatic hydrocarbons.
 52. The system ofclaim 50, wherein the hydrocarbon comprises at least one alkane.
 53. Thesystem of claim 52, wherein the at least one alkane comprises butane,methane, ethane and/or propane.
 54. The system of claim 52, wherein theat least one alkane comprises butane.
 55. The system of claim 54,wherein the butane is provided as a butane substrate comprising butaneas the most prevalent compound of the substrate.
 56. The system of claim54, wherein the butane is provided as a butane substrate comprising atleast about 10 weight percent butane.
 57. The system of claim 54,wherein the butane is provided as a butane substrate comprising at leastabout 50 weight percent butane.
 58. The system of claim 54, wherein thebutane is provided as a butane substrate comprising at least about 90weight percent butane.
 59. The system of claim 52, wherein the at leastone alkane comprises methane.
 60. The system of claim 52, wherein the atleast one alkane comprises ethane.
 61. The system of claim 52, whereinthe at least one alkane comprises propane.
 62. The system of claim 50,wherein the hydrocarbon is introduced to the hydrocarbon-utilizingbacteria intermittently.
 63. The system of claim 50, wherein the metalcomprises gold, silver, platinum, palladium, copper, zinc, nickel and/oruranium.
 64. The system of claim 50, further comprising: a source ofoxygen; and an oxygen injection system in communication with the oxygensource and the support material.
 65. The system of claim 64, wherein theoxygen is supplied in the form of air or substantially pure oxygen.